There is a way to turn BSP to MAP, it's called decompiling. But it's a really bad idea. When you decompile a map you lose all the texture alignment and scaling, every brush turns into at least 6 separate brushes. It's impossible to compile a map after it's been decompiled.

If you want to, you can decompile and fix all the brushes and textures manually. I think the program is called BSPtoMAP.